The art of making and developing new uses for thermo optic devices continues to emerge. Presently, thermo optic devices are used as filters, switches, multiplexers, waveguides, and a host of other semiconductor and optical transmission devices.
With reference to FIGS. 1A and 1B, a thermo optic device in accordance with the prior art is shown generally as 110. It comprises a cladding 115 that includes an upper cladding 114 and a lower cladding 112. A core 116 is defined by the cladding and is generally formed of a material having a higher or lower refractive index than that of the cladding. The core 116 may, for example, define an optical waveguide, such as a Y-shaped optical splitter having an input waveguide 122 and two output waveguides 124, 126. The core 116 together with the cladding 115 are sometimes referred to as a grating and are disposed on a substrate 118. The substrate may be formed of silicon but is not required to be. A heater 120 is disposed adjacent to the cladding 115.
During use, a control element (not shown) delivers current to the heater 120, to change an optical characteristic of the thermo optic device. For example, in a Bragg grating formed with a polymer grating, when current is delivered to heater 120, the refractive index of the polymer will change as a result of the thermo optic effect. In turn, this refractive index change affects the wavelength of light that satisfies the known Bragg reflective condition so that a different wavelength is now Bragg reflected in the optical waveguide.
If the process is repeated at another temperature, which is a function of current delivery and heater characteristics, another wavelength will satisfy the Bragg reflective condition. In this manner, the thermo optic device 110 is made tunable. Such a device will normally be operated in a steady state condition so that a single wavelength will satisfy the Bragg reflection condition over a given time interval.
With reference to FIGS. 1C and 1D, a portion of the thermo optic device 110 is shown in greater detail. In particular, the heater 120 is formed with contacts 121, 123 and conductors 131, 133 to, ultimately, connect to the control element during use.
Unfortunately, the heater 120, together with its associated contacts 121, 123 and conductors 131, 133, requires three fabrication masking steps to form with conventional processes, i.e., one masking step to form the heater, one to form the contacts, and one to form the conductors. This unnecessarily complicates manufacturing and wastes resources and finances.
Accordingly, the thermo optic arts desire improved heaters that are cheaper and quicker to produce, e.g., formed by fewer mask counts, without any corresponding sacrifice in quality, reliability or longevity.